Cosmic accidents: How we avoided the void

We wouldn’t exist if our cosmic neighbourhood had been just a bit less dense than average during the tumultuous moments after the big bang

It began with a bang. What cosmic coincidences preceded our universe’s birth are in the realms of speculation. Suffice it to say that some 13.75 billion years ago – give or take a yoctosecond – the cosmos was deciding what to be when it grew up.

“Much bigger”, if the most popular model of the universe’s beginnings is to be believed. According to the theory of inflation, the newly born universe was suffused with something called the inflaton field, which drove an exponential expansion of the cosmos for a period of about 10-32 seconds, stretching it flat and uniform in the process.

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That usefully accounts for some otherwise tricky-to-explain characteristics of our universe, but the real point of interest is that the inflaton field, although essentially uniform, was not quite identical in each bit of space. Chance quantum fluctuations made it slightly more dense here, and just a little less dense there. It is lucky for us that this was so, and that here and there were that way around. If here had been a bit less dense than the average, then we would not exist. For a hundred million light years in all directions around where we would not be, there would be a dark and lifeless void.

This one microscopic quantum of noise, amplified by gravity, eventually grew into a huge agglomeration of galaxies …